Selecting vertices within a box defined by exact coordinates
You can do this using python.

Open up a text editor in Blender and paste the following script.

import bpy, bmesh
from mathutils import Vector

# checks if a supplied coordinate if in the bounding box created by vector1 and vector2
def IsInBoundingVectors(vector_check, vector1, vector2):
    for i in range(0, 3):
        if (vector_check[i] &lt; vector1[i] and vector_check[i] &lt; vector2[i]
            or vector_check[i] &gt; vector1[i] and vector_check[i] &gt; vector2[i]):
            return False
    return True


def SelectVerticesInBound(object, vector1, vector2):
    # get the mesh data from the object reference
    mesh = object.data

    # get the bmesh data
    if mesh.is_editmode:
        bm = bmesh.from_edit_mesh(mesh)
    else:
        bm = bmesh.new()
        bm.from_mesh(mesh)

    # cycle through all vertices
    for vert in bm.verts:
        # check if the vertice is in the bounding vectors
        # if yes, select it
        # if no, deselect it
        if(IsInBoundingVectors(vert.co, vector1, vector2)):
            vert.select = True
        else:
            vert.select = False

    # update bmesh to mesh
    if bm.is_wrapped:
        bmesh.update_edit_mesh(mesh, False, False)
    else:
        bm.to_mesh(mesh)
        mesh.update()
    # trigger viewport update
    bpy.context.scene.objects.active = bpy.context.scene.objects.active



# get the active object from the scene
active_object = bpy.context.scene.objects.active

# ensure that there is an active object
if (active_object != None):
    # call the method to select all vertices in bounding box vectors
    # object             the object to operate on
    # vector 1           the first coordinate of the bounding box
    # vector 2           the second coordinate of the bounding box
    SelectVerticesInBound(active_object, Vector((0, 0, 0)), Vector((1, 1, 1)))


The coordinates for the two vectors are supplied in the last line, which calls the method. Input your coordinates, select a mesh in object mode and press Run Script or &#9095; AltP to run the script.

I have included comments explaning the code. Additional resources.


Get Vertex Positions
Properly get and update Bmesh objects
Select Vertices


Note: Somehow vertices don't get deselected when the object is in object mode. Maybe an experienced python coder can help us out here.